Intersections serve a critical role for traffic flow management. In this regard, an intersection having a traffic signal associated therewith provides well-defined intersection movement state control strategies to insure vehicle capacity within the intersection is not exceeded and to increase the likelihood that vehicles will propagate safely through the intersection.
Each traffic signal implements an assigned signal phase and timing (SPaT) control strategy. This SPaT control strategy defines the different signal phases of the traffic light, such as the red, yellow and green signal phases, as well as the relative timing of each phase. In some instances, the relative timing may be predefined such that each of the red, yellow and green signal phases has a respective predefined length. Alternatively, other traffic signals may be actuated, such as by traffic approaching and/or passing through the intersection. For a traffic signal that is actuated, the timing of the different signal phases may vary, such as between predefined maximum and minimum values, based upon the traffic flow therethrough.
Based upon information regarding the SPaT control strategy of a traffic signal as well as information regarding the intersection controlled by the traffic signal including the number of lanes and the intended direction of travel through the lanes, various services may be provided. For example, traffic service providers or traffic management agencies may utilize this information to provide energy savings by reducing unnecessary vehicle acceleration and deceleration by routing vehicles and timing the approach of the vehicles to intersections in such a manner as to pass through more intersections without having to stop at a red light. Additionally, this information may be utilized in order to dynamically adjust navigation plans in order to reduce travel time and/or to more accurately predict the time of arrival at a destination. Still further, this information may be utilized to provide safety warnings, such as alerts to pedestrians having sight limitations who are crossing an intersection.
The information relating to SPaT control strategies for traffic lights and information regarding intersections controlled by the traffic lights may be provided to mobile platforms carried by vehicles traversing the roadways via a cellular network or via dedicated short range communications (DSRC). Although the delivery of this information via a cellular network allows the information to be provided while the vehicles are a long distance from the intersections, cellular networks may suffer from latency issues, such as by having increased latency relative to DSRC, such as a result of backend processing of the information regarding the signal phase and timing of the traffic lights, particularly the more extensive processing required of the information for traffic lights that are actuated. As the traffic phase and timing information for traffic lights is time-sensitive since the signal phases of the traffic lights are repeatedly changing, the latency introduced by a cellular network may prove to be detrimental.
DSRC generally has reduced latency relative to cellular communications. In addition, DSRC is designed, at least in part, to transmit SPaT information for traffic signals. In this regard, the SAE J2735 standard in the DSRC message set dictionary defines the SPaT format which describes the current state of a traffic signal system and the phases corresponding to specific lanes of the intersection. In addition to the SPaT information, the SAE J2735 standard defines the map data format describing the static physical geometric layout of one or more intersections. The map data format is used to convey many types of geographic road information. The map data along with the SPaT information describes an intersection and its current control state through the mapping of lane information for each lane to the corresponding traffic signal group identifier.
Unfortunately, DSRC has a relatively short range, such as a few hundred yards to 1 kilometer. In this regard, DSRC broadcasts signals at a 5.9 gigahertz radio frequency and, as a result, is subject to more environmental interference than signals transmitted by other types of networks, such as cellular networks, that communicate on a point-to-point basis. As a result, the information relating to the traffic signals and corresponding intersections that is transmitted via DSRC may be degraded or even completely blocked, such as due to interference, in some instances. In any event, the interference effectively limits the range at which the traffic signal and intersection information may be received by mobile platforms carried by vehicles. In this regard, to reliably receive information regarding a traffic signal and the corresponding intersection transmitted by a DSRC transmitter proximate the intersection, the vehicle must be relatively near the intersection, while similar information may be received via a cellular network much further from the intersection. Additionally, DSRC has a more limited bandwidth capacity than a cellular network. As such, in instances in which many vehicles are in or near an intersection, such as during rush hour, during or following an incident, such as a traffic accident, at the intersection, during an outage of the traffic signal, etc., the information regarding the traffic signal and the corresponding intersection may not be able to be effectively transmitted, at least not to all of the vehicles in or near the intersection as a result of the limited bandwidth capacity of DSRC.
Thus, while information regarding traffic signals, such as SPaT information, and information regarding the corresponding intersections may be useful for a variety of applications, it has been challenging in some instances to reliably receive the information in a timely manner with mobile platforms in or near an intersection due to various issues associated with the networks via which the information is transmitted.